Fluid rectifier



Aug. 6, 1963 J. c. FISHER 3,099,998

FLUID RECTIFIER VI O f INVENTOR.

g T JOHN c. FISHER BY FIG.4

ATTORNEYS J. C. FISHER FLUID RECTIFIER Aug. 6, 1963 4 Sheets-Sheet 2Filed April 11, 1960 FIG.6

R m w w. s F C N H o J E T T 0 BY I mlrdL/ WW FIG.7

ATTORNEYS Aug. 6, 1963 J. c. FISHER 3,099,998

FLUID RECTIFIER Filed April 11, 1960 4 Sheets-Sheet 3 FIG.8

+ V O 3 i- I T 2T INVENTOR.

2 2 JOHN C. FISHER ATTORNEYS Aug. 6, 1963 J. C. FISHER Filed April 11,1960 FLUID RECTIFIER 4 Sheets-Sheet 4 Z 4 ii}; \l g /56 55 54 L 58FIG.|I

ATTORNEYS United States Patent 3,099,998 FLUID RECTIFIER John C. Fisher,Cambridge, Mass assignor to Am Dyne Trust, a trust of MassachusettsFiled Apr. 11, 1960, Ser. No. 21,412 3 Claims. (Cl. 137525.3)

This invention relates to a novel and improved fluidrectifier valve foruse in pumping devices of the type or types which produce areciprocating or alternating flow of fluid internally and employ checkvalves or the like to convert this reciprocating flow to aunidirectional flow. This application is a continuation-in-part of mycopend ing application Serial No. 636,597, filed January 28, 1957, nowabandoned.

Examples of fluid pumps of the type with which the invention isconcerned are: 1) single-cylinder piston pumps; (2) multi-cylinderpiston pumps; (3) diaphragm pumps; (4) accelerator-tube pumps (sometimescalled inertia or liquid-piston pumps) of the type described in mycopending patent application Serial No. 553,015, dated December 14,1955, now Patent No. 2,936,713; and (5) piston-tube pumps of the typedescribed in my U.S. Patent No. 2,898,858, issued August 11, 1959. Suchpumps when operated at low frequencies can satisfactorily employrectifier valves of the long-familiar ballcheck type. This type of valvehas proved very reliable over a long period of use and evolution inlow-frequency reciprocating pumps. However, when such pumps are operatedin the frequency range from 20 cycles per second upward, the use ofball-check valves causes the volumetric efliciency of these pumps todecline steadily with increasing frequency. This is so because the checkelement in the ordinary ball-check valve is essentially a free masscoupled to the moving stream only by frictional forces. To cause such amass to reciprocate through a fixed displacement requires a force whichincreases in proportion to the square of the frequency. Thisparabolically increasing force can be provided only by a relativevelocity between the stream and the check element, such that the streammoves faster (absolute velocity) than the check element. The situationcan be improved somewhat by the use of a hollow check element to reduceits mass, and by employing a shape which has a high drag coeflicient,but inevitably, as frequency increases, the displacement of the checkelement from its seat lags further and further behind the velocityvariation of the stream. The result is that considerable backflow occursthrough the valve, and the volumetric efliciency of the pump declinesprogressively toward zero. Further disadvantages of thefree-check-element type of rectifier valve are the noisy operation andthe mechanical hammering of the check element against the seat and theforward stop as the operating frequency rises. The time-honored means bywhich this problem has been attacked has been the use of a springelement so arranged as to push the check element against the seat. Thespring thus provides an additional force over and above the frictionaldrag acting to drive the check element back onto the seat when theforward stream reverses. By this means the time-lag between flowreversal and closing of the valve can be reduced.

However, the mere addition of a spring does not reduce the overall timelag between check valve displacement and the velocity variation of thefluid to the extent desired for optimum operation and will, of course,tend to increase the time lag on opening of the valve. This is partlydue to an increase in eflective mass of the system caused by theaddition of the spring. Also when the check element is immersed in afluid, and particularly a liquid, the movement of the check elementthrough the 3,fl99,998 Patented Aug. 6, 1963 ICE fluid results in achange in speed or direction of the fluid, resulting in an inertialforce on the check element which affects system behavior in the same asif the mass of the check element had been increased.

To some extent, this mass-loading of the valve system can be reduced bystreamlining the check element and the spring. It can also be partiallycompensated for by increasing the stiffness of the spring. However,simply increasing stiifness is not entirely beneficial, because itincreases the forward pressure difference necessary to open the valve,and also the forward pressure drop with valve open at any given flowrate. This causes a loss of energy from the flowing stream, and it alsocauses the volumetric efiiciency to suffer if such a valve is used onthe intake side of a pump, because the forward pressure drop causes afall in the density of a flowing gas or a possibility of cavitation in aflowing liquid.

Accordingly, it is the object of this invention to provide a novel andimproved rectifier valve for use with fluid pumping systems of the typeproviding an alternating out put fluid flow which will operate insubstantial time phase relationship with the frequency of velocityvariation of the output fluid flow thus materially reducing, if notsubstantially eliminating, back flow through the valve; which willoperate quietly and with a minimum of wear; which will require arelatively small pressure drop to effect actuation thereof in an openingdirection; and which is of a relatively simple construction and Willprovide an extended trouble-free service life.

In the drawings:

FIG. 1 is a diagrammatic representation of an exemplary single actingpiston pump system incorporating rectifier valves;

FIG. 2 is a graphic representation of the velocity-time relationship ofthe movement of the piston of the pump of FIG. 1;

FIG. 3 is a graphic representation of the velocity-time relationship ofthe output flow of the pump of FIG. 1;

FIG. 4 is a graphic representation of the velocitytime relationship ofthe input flow of the pump of FIG. 1;

FIG. 5 is a diagrammatic representation of an exemplary double actingpiston pump system incorporating rectifier valves;

FIG. 6 is a graphic representation of the velocity-time relationship ofthe movement of the piston of the pump of FIG. 5;

FIG. 7 is a graphic representation of the velocity-time relationship ofthe output fluid flow of the pump of FIG. 5;

FIG. 8 is a diagrammatic representation of an ex emplary three-phasereciprocating fluid pumping system incorporating rectifier valves;

FIG. 9 is a graphic representation of the velocitytime relationship ofthe movement of the pistons of the pumps of FIG. 8;

FIG. 10* is a graphic representation of the relationship of the velocityvariation in the output fluid flow in the system of FIG. 8 to the threepiston velocities;

FIG. 11 is a cross sectional view of an alternative form of a rectifiervalve;

FIG. 12 is a cross sectional view substantially along the line 17-17 ofFIG. 11;

FIG. 13 is a cross sectional view of an embodiment of a rectifier valveincorporating the present invention; and

FIG. 14 is a cross sectional view substantially along the line 19-19 ofFIG. 13.

In order to appreciate the many physical arrangements of pump systemswith which this invention is concerned, reference will now be made toFIGS. 1-10 which relate to the more well-known configurations which canbe used to pump liquids or gases. In each case, the pumping deviceitself produces an internal fluid displacement and velocity which isessentially alternating or reciprocating, and rectifier valves areprovided to operate upon this alternating flow to produce in theexternal fluid circuit an essentially unidirectional, but usuallypulsating flow. For simplicity, the pumping elements have been shown aspistons, but it is to be understood that other structures such asdiaphragms, accelerator tubes, etc., could also be used to motivate thefluid.

FIG. 1 shows the schematic arrangement of a single acting piston pumpfor fluids. For simplicity, a crankand-connecting-rod drive is shown,but, as will be apparent, a cam mechanism, an electrodynamic vibrationmotor, etc., could be employed. An intake pipe 1 leads the fluid throughan intake rectifier valve 2 into a cylinder 3. Received in the cylinderis a piston 4 actuated by means of a connecting rod 5 which is in turndriven by a crankshaft '6. From the cylinder 3, on the discharge strokeof the piston, the fluid emerges via rectifier valve 7 and dischargepipe 8. The time-variation of the piston velocity V; is substantially asine wave as shown in FIG. 2, and if the rectifier valves perform theirfunction effectively, the variation in the velocity V of the fluid inthe intake pipe and the variation of the velocity V in the dischargepipe will, as shown in FIGS. 3 and 4, respectively, be substantially asinusoid in which only the positive half-wave remains, the negativehalf-waves having been removed by the action of the rectifier valves. Itis to be noted that the positive half-waves in pipe 1 represent aperiodic function which is displaced positively on the time scale byone-half period, T/ 2, relative to the positive half-wave train in pipe8. This is so because the piston is single-acting, and the intake pipecan conduct fluid forward only when the discharge pipe is notconducting, and vice-versa.

In regard to FIG. 1, it should also be noted that within the volume.swept through on each complete cycle by the top of the piston (shownshaded in FIG. 1) there is a purely alternating flow of the fluid aslong as the liquid or gas remains-in contact with the piston top(cavitation does not occur, with a liquid). If there were no valves 2and 7, this purely alternating flow would extend from the intake pipethrough the pump to the discharge pipe, and no useful external fluidtransfer would occur. The action of the valves converts the purelyalternating fluid velocity at the piston top to a unidirectional,pulsating fluid velocity in each of the pipes 1 and 8. Hence the termrectifier valve" is fully justified in reference to valves 2 and 7.

FIG. 5 shows a double-acting piston pump. This type of pump is oftenpreferable to the single-acting variety, because it produces a greaterdischarge for the same piston displacementrate (in terms of volume perunit time), and its external flow pulsations are smaller in relation tothe average flow than those of the pump in FIG. 1. In FIG. 5, a piston 9divides a closed cylinder 10 into two identical chambers 11 and 12. Eachchamber is traversed by an extension of a shaft 13 which carries piston9. The shaft 13 is driven by a connecting rod 14 and a crankshaft 15 insuch a way as to produce a substantially sinusoidal piston velocity, Vas shown in FIG. 6. The chamber 11 is connected via an intake rectifiervalve 18 to an intake pipe 16, and via a discharge rectifier valve to adischarge pipe 21. Similarly, chamber 12 is connected via an intakerectifier valve 17 to a pipe 16, and via a discharge rectifier valve 19to a pipe 21. Inflow of fluid to the pump is via a pipe 16 and outflowis via a pipe 21. By analogy with the rectification of alternatingelectric current, it may be said that the rectifier valves 17, 18, 19,and 20 are connected in a single-phase, full-wave bridge arrangement.This bridge arrangement of valves serves to convert the purelyalternating fluid velocity at each end face of piston 9 into aunidirectional, pulsating fluid velocity V at the intake pipe and V atthe discharge pipe. The timevariation of fluid velocity is here the sameat both pipes 16 and 21, and is essentially a rectified full-sinusoid.It should be noted that as shown in FIG. 7 there are two majorpulsations of fluid velocity in every period T, where there was but onein the pump system of FIG. 1.

FIG. 8 shows a 3-phase, single-acting pump system. The chief advantageof this arrangement, and its logical extensions to higher numbers ofphases, is the reduction in the magnitude of the external flowpulsations relative to the average flow. The system of FIG. 8 isessentially three pumps like the pump of FIG. 1, with their respectiveintake pipes in parallel and their respective discharge pipes inparalley. A crankshaft 23 drives the pistons 27, 28, and 29 throughconnecting rods 24, 25, and 26, respectively. The three connecting rodsare driven by the same crankpin, and the pistons they control arearranged to move back and forth along axes which are spaced apart aroundthe center of the crankshaft. As shown in FIG. 9, the time-phasedifference between the velocity of any one piston and the next is thus/s-cycle. If a higher number of phases had been used, for example, six,then the phase shift between successive pumping elements would beAs-cycle or 60. Cylinders 30', 31, and 3% are each associated with anintake rectifier valve 33, 35, and 37, respectively; and a dischargevalve, 34, 36 and 38, respectively. Flow enters the common intake pipe39, divides equally among the three pumping elements, and emerges from adischarge pipe 40. It should be noted here that, as shown in FIG. 10,the major frequency of pulsation in the flow through pipes 39' and 40 issix times the piston frequency, there being six major pulsations in thisflow in every period T.

It will be readily apparent that many other pumping arrangements of thisgeneral type are possible. The foregoing examples merely serve to showsome of the more important pumping systems in which rectifier valves areemployed.

Ideal behavior for a rectifier valve in a fluid pump of the type withwhich this invention is concerned is as follows: the valve should openwith the minimum possible forward pressure difierence :at the instantwhen forward fluid velocity rises from zero; the opening of the valve,that is the displacement of the check element from its seat, shouldincrease continuously as the forward fluid velocity increases; theopening of the valve should decrease continuously as the forward fluidvelocity diminishes; and the valve should just be seated again at thetime when the forward fluid velocity reaches zero and would, in theabsence of the valve, reverse in direction. Stated more concisely, therectifier valve should cause minimum forward pressure drop in the fluidstream, and its displacement ofi the seat should be exactly intime-phase relation with the forward fluid velocity. Secondary criteriaof proper behavior are: the valve should have but one degree of freedom,that is it should be constrained against all motions other than thedirect one on and off the seat parallel to the average direction of thefluid stream; and it should strike the seat on closing with the leastpossible momentum. This latter condition implies that the effective massof the valve element must be as low as possible, and that its backwardvelocity at the instant of closing be as near zero as possible. Finally,the back-and-forth motion of the valve element should occur with aminimum of rubbing or sliding contact between solid surfaces. This lastconsideration is important because it affects the rate of mechanicalwear of the valve parts, and it partially determines the forwardpressure drop across the valve since friction in the valve must beovercome by an externally applied force in order to keep the valveelement moving.

I have found that the above criteria fora rectifier valve which willsatisfactorily operate with reciprocating pumps operating in thefrequency range from 20 cycles per second up to as high as 250 cyclesper second, is met in a valve having as its principal operative elementa substantially flat, cantilever reed, of solid highly resilientmaterial not subject to permanent set in normal operation of the valve,with one end of the reed being rigidly secured and the other endcovering an opening or port through which fluid may flow in such adirection as to push the free end of the reed away from the port, butnot in the opposite direction, and with the reed having a lowestundamped natural frequency, when immersed in the fluid, which is greaterthan the frequency of the velocity variation of the fluid passingthrough the valve. The effective static stiffness of the reed forforward deflections (off the seat) must be as low as possible consistentwith the requirement that the immersed undamped natural frequency of thereed 'be at least equal to but preferably greater than the frequency ofthe variation in fluid velocity. All other factors being equal, I havefound that those rectifier valves which have the highest ratio ofimmersed undamped natural frequency to effective forward staticstiffness, yield the highest volumetric efficiency when used to rectifythe intem-al fluid velocity produced by reciproeating pumps like thoseshown in FIGS. 1, and 8. Volumetric efiiciency of a reciprocating pumpis defined as the ratio of the average fluid volume per unit timedelivered out the discharge pipe, to the total volume per unit timeswept through inside the pump by all the motivating elements, whetherthey be pistons, diaphragms, etc.

Although it is possible to compute analytic-ally the lowest undampednatural frequency of a cantilever reed when immersed in air or anycommon gas, it is extremely diflicult to compute by purely theoreticalmeans the lowest undamped natural frequency of such a reed when immersedin a liquid. The lowest natural frequency of the system is proportionalto the square-root of the ratio of effective systems stiffness (springrate), measured statically, to effective system mass. With the reedimmersed in a fluid the effective mass of the reed is increased; this isnot serious with gases, but with liquids it considerably raises theeffective mass of the reed. This is so because the check element cannotmove through the liquid without causing some change in the absolutevelocity thereof, either a change in speed (rate) or a change indirection. This change of velocity is responsible for an inertial forceon the reed, and this inertial force affects the system behavior inexactly the same way as if the mass of the reed had been increased. Thebest method, from a practical point of view, is to design the reed onthe basis of gas immersion, and to modify the design by use of empiricalfactors derived from tests on liquid-immersed reeds of similarconstruction; In most cases, I have found that those reeds which exhibitthe highest ratio of lowest undamped natural frequency to effectivestatic stiffness in air, also exhibit the highest ratio in liquids likewater, oil, kerosene, etc. which are commonly encountered in industr-ialpumping systems.

The cantilever valve reed may be made with uniform width and thicknessalong its entire length, or the width and/ or the thickness may bevaried in some definite manner along the length. The end of the reedwhich covers the valve port may be made flat, or it may be furnishedwith a protuberance of some sort which serves to cover the valve port.The fixed end of the reed may be clamped by welding, bolting, riveting,or any of the commercially accepted means of fastening two solid objectstogether. The material for the reed may be any of several homogeneousmaterials such as steel, copper, brass, aluminum, titanium, Monel, andother suitable metals; or unreinforced plastics likepoly-tetrafluoroethylene (Teflon) or poly-methylmethacrylate(Plexiglas); or reinforced plastics like melamine-bonded wovenfiberglass fabric and a whole family of similar composite materials.

In each complete rectifier valve there may be but one cantilever reedand associated valve port, or there may be several such reeds and portsarranged in parallel so as to divide the fluid flow to obtain a greatereffective port area and a reduced forward fluid velocity. The valve reedmay be clamped in such a way that there is a definite preloading in theclosed position, i.e. the reed is under some bending stress when seated.This helps to reduce back leakage through the valve when the reed is inclosed position, but it also increases the forward pressure drop throughthe valve. The flow through the valve port may be in a direction whichis substantially perpendicular to the general plane of the valve reedwhen the valve is closed. However, I liave found by experiment that itis often beneficial to construct the valve so that the reed when inseated position is obliquely inclined to the average direction of theforward-flowing fluid. It is clearly apparent that any design ofrectifier valve which works well in a singlephase pumping device likethat of FIG. 1 will also work well in any polyphas'e pumping device likethat of FIG. 8. Hence, what has already been said, and the descriptionwhich follows, are equally relevant for the operation of rectifiervalves in both single-phase and polyphase reciprocating pumps.

Although exact analytical relationships cannot be derived for theimportant practical case of liquid-immersed rectifier valves, a study ofthe case of an air-innnersed cantilever reed having uniform width andthickness along its length will reveal the important parameters of theproblem. Assume that a reed is mounted so that one end is rigidlyclamped to a stationary support and the opposite end is free to move ina direction perpendicular to the general plane of the reed. As long asthe deflection of the free end of the reed does not exceed 20% of thefree length of the reed, which it will seldom do in practical cases, thefollowing analytical relationships are valid. The effective staticstiffness of the reed is defined as the static fomce appliedperpendicular to the plane of the reed at its free end, divided by thedeflection which results there and is expressed as:

1 d 3 (1) K ED( where K=the effective (free-end) static stiffness of thereed, in

units of (Force) (Length);

E=Youngs modulus of elasticity for the reed material,

in units of (Force) (Area) D=the width of the reed, in of (Length);d=the thickness of the reed, in units of (Length); L=the free length ofthe reed, in units of (Length). The undamped natural frequency of thereed in air, in its lowest natural mode of transverse vibration, i.e.that mode in which every point along the free length !Of the reed at anyinstant is deflected to the same side of the rest position, is given byi (2) w,, 1.0162 w where w -=the lowest undamped natural frequency inair, in units of (Radians) (Time);

g=-the eaiths gravitational acceleration, in of (Length)/(Time) w=thespecific weight of the reed material, in units of (Force) (Volume).

From Equations 1 and 2, we may derive the ratio of unclamped lowestnatural frequency in air to effective static stiffness of the reed:

stress may reach if the reed is to survive a predetermined number ofcycles of opening and closing. This is generally referred to as anendurance If we denote the endurance by S then we may arbitrarily writea new criterion for a rectifier valve of the cantileverreedtype, namelythe product of the ratio given by Equ tion 3 land endurance limit:

as, 4.065JL (4) K Dd Se Ew On the basis of Equation 4 :a preferredchoice of material is a laminated fiberglass sheet such as N.E.M.A.Grade G- lO, because it has a low modulus E by comparison with metals,low specific weight w' by comparison with metals, but a high endurancelimit S comparable to that for low-carbon steel. Of course, such amaterial cannot be used except where it satisfactory resistance tochemical attack by the fluid to be pumped.

If a cantilever reed like that discussed above be subjected to aperpendicular force at its free end which varies according to therelation (5) siu wt, where =the instantaneous value of the force, inunits of (Force);

f=th-e crest or peak value of the force, (Force); w=the frequency of theforce variation, in units of (Radians) (Time); t=time measured trom theinstant at which the force first increases positively from zero, (Time);

then the free end of the reed will experience a displacement from restposition, a velocity, and an acceleration. Each of these kinematicvariables will have a sinusoidal time-variation, but they will bedisplaced, respectively, by phase-shifts of one-quarter cycle fiuom oneto the next, the acceleration being first in time-phase, the velocityone-quarter cycle behind acceleration, and the displacement directlyopposite in phase to the acceleration. In the absence of frictionalforces acting merely to halt the motion of the reed, the reed willbehave either like a pure-mass element or like a pure-stillness element,depending upon whether its lowest natural frequency ca is lower orhigher, respectively, than the frequency w of the disturbing force. Ifca be lower than to, then the acceleration of the reed will be intime-phase with the disturbing force, and in regard it will behaveessentially like the free mass of 1a hall-check valve, except that itsapparent dynamic mass will be less than its true mass. Because of thereduction of apparent dynamic mass below true mass, the acceleration ofthe reed at the free end be greater than it would if the force f werestatically applied, but the displacement of the free end from restposition is just one-half cycle out of time-phase with the disturbingforce. Since one of the criteria of good performance for a rectifiervalve is that the displacement of the check element from rest positionmust be in timephase with the forward velocity of the fluid stream (andthe drag force due to the stream is exactly in time-phase with the fluidvelocity), then clearly a reed valve whose lowest undamped naturalfrequency (a is lower than the frequency w of the fluid-velocityvariation cannot perform satisfactorily. This has been verified by me byexperiments with reed valves of many shapes and sizes.

On the other hand, if the lowest undamped natural frequency of the reedis greater than the frequency of the force variation (w w), thedisplacement of the reed will be in time-phase with the disturbingforce. Because the apparent dynamic stiffness at the free end of thereed will always be less than the static effective stiffness, thedisplacement of the free end will be greater than it would if the, forcef were statically applied. However, because of the time-phasecoincidence of tip displacement and disturbing force, a cantilever reedwhose lowest undamped natural frequency is greater than the frequency ofthe fluid-velocity variation is suitable as an element for a rectifiervalve. If the apparent dynamic stillness at the free end of the reed bedenoted by K,,, then the relationship of this parameter to staticeffective (free-end) stillness is From Equation 6 it can be seen thatwhen w=w the apparent dynamic stillness is zero, and the only restraintupon the displacement, velocity, and acceleration of the free end of thereed is the internal (molecular) friction, which is never zero in anyknown material, although it is small enough in most spring materials tobe ignored for many practical purposes. This is a. condition ofresonance, and the tip of the reed would undergo a very largealternating displacement. In most materials this would cause an earlyfatigue failure because of the very large internal bending stresses.However, at the exact condition :of resonance, the velocity of thereed-tip would be in phase with the disturbing force, and again the reedwould be unsatisfactory for use as \an element in a rectifier valve. Itshould be noted that when such a reed is immersed in a fluid, thefrictional force IOD. the reed due to the velocity of the fluid relativeto the reed is the disturbing force, and not a damping force. 7

The preceding analysis serves to substantiam statement that anyspring-loaded rectifier valve having only one degree of freedom willyield high volumetric efiiciency when used with a reciprocatingpumpabove 20 cycles per second only if the lowest unclamped naturalfrequency of the moving system in the valve is greater than thefrequency of velocity variation of the fluid stream. The foregoinganalysis was directed toward valve elements of the cantilever-reed type,but it is equally valid for the case of a spring-loaded ball-checkvalve, provided that the correct equations are used for effective staticstiffness and natural frequency.

I have found that maximization of the ratio given by Equation 3, namelyw /K, is best accomplished by the use of a cantilever reed whose width Dand thickness d each decrease in some regular llashio-n from maximumvalues at the clamped end of the reed to values at the free end. Inevery case such a tapering reed will have a higher ratio to /K than areed of the same material having the same maximum width and thicknessbut of constant width and thickness along the free length. Theanalytical proof of this is very difficult, because it requires thesolution of the differential equation of the elastic curve of acantilever beam with variable cross section. differential equation is dy EI M where I =the moment of inertia of the cross section of the beam,

in units of (Length) y=ldfl0tl0fl from rest position of any point on thefree length of the beam in a direction normal to the rest plane of thebeam, (Length);

x= distance along the free length of the beam, measured parallel to therest plane from any convenient point on the beam (Length);

M =bendin-g moment acting on any cross section of the beam in a planenormal to the rest plane of the beam, in units of (Force) (Length).

For a uniform beam (constant width and thickness),

Equation 7 can readily be solved, and it leads to the derivation ofEquations 1 and 2. However, for a tapered beam, Equation 7 becomes asecond-order differential equation with a variable coefficient, which isdifficult to solve without the aid of a computing machine. The variablefactor is I, which for a rectangular cross section is given by 9 Inspite of the analytical difficulties in the solution of Equation 7 fortapered beams, it can readily be demonstrated by experiment that theratio w /K is higher for tapered beams than those of the same material,same maximum width and thickness, and constant width and thickness.

In the embodiment of FIGS. 11 and 12, a valve body in the form of arigid duct 53 having a rectangular or square cross section is divided bya tight-fitting rigid insert 54 into an upstream passage 58 and adownstream pass-age 59. The valve also includes a flat cantilever reed55, of constant thickness and Width, whose fixed end is securely clampedby screws 57 between clamping plate 56 and a flat mating shelf in insert54. Fluid flow can occur only in the direction shown by the arrows,namely from passage 58 to passage 59. In certain applications therectifier valve may be required to Withstand high pressure diflerencesin the reverse or back flow direction of flow through the valve.Accordingly, it may be necessary to support the reed 55 on its upstreamside. In the embodiment of FIGS. 11 and 12 this support of the reed isprovided by the top wall of the passage 58. As can be seen from thedrawings, the reed 55' is in overlying engagement with the top wall ofthe passage 58, and the top of the passage 58 is provided with aplurality of closely spaced openings for the flow of fluid therethrongh.

In the embodiment of FIGS. 13 and 14 the valve comprises a body formingduct 6%} having rigid walls and rectangular cross section. The duct 60is divided by a tight-fitting rigid insert 61 into an upstream passage63 and a downstream passage 64. Passage 63 is of rectangular section,and at its downstream end, its upper wall is cut away to form atriangular aperture. This aperture is covered on its downstream side bya cantilever reed 62, which is securely clamped at its upstream endbetween a clamping plate 65 and a mating flat shelf formed in the insert61. Screws 66 are set into tapped holes in the insert 61 to provide theclamping force. The reed 62 has constant width and thickness under theclamping plate 65, but from the downstream edge of the plate 65 outward,the thickness of the reed tapers linearly to a minimum at the free end.Similarly, the width of the reed 62 tapers linearly from the clampededge outward to the free end. For reasons of simplicity in forming thereed and the seat, it is desirable to put all the taper on thedownstream (upper) face of the reed. However, this is not an absolutenecessity, and the taper could be divided in any reasonable mannerbetween the two faces. Similarly, the taper in width could all be put onone edge, or could be divided in any way between both edges. In anyevent it is necessary only that the bottom face of the reed engage therim of the orifice at all points around its periphery, and that theedges of the reed project just beyond the mating edges of the orifice,in order to prevent backflow when the reed is seated.

The advantage of the construction shown in FIGS. 13 and 14 over thatshown in FIGS. 11 and 12 is that the ratio ca /K is highest for thetapered reed (other things being equal), and yet the escape area for thefluid around the edge of the reed is large so that the forward pressuredrop is reduced.

It should be apparent from the above that the specific differences instructure between the embodiments described above are merelyillustrative of the many variations in construction of the rectifiervalve which are possible within the scope of this invention. Further itshould be apparent that each of the valves described above could bemodified in accordance with the teachings of another of the embodimentsdescribed and that additional modifications of and variations incantilever sup ported reed rectifier valves of the type described couldbe made without departing from this invention, the critical limitationbeing that the lowest undamped natural frequency of the reed whenimmersed in a fluid passing 1% through the valve must be greater thanthe frequency of the velocity variation of the fluid flowing through thevalve.

Inasmuch as many changes could be made in the above construction andmany apparently widely different embodiments of this invention could bemade without departing from the scope thereof, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the language in the following claims isintended to cover all of the generic and specific features of theinvention herein described and all statements of the scope of theinvention which, as a matter of language, might be said to falltherebetween.

Having thus described my invention, I claim:

1. In a pumping system of a type providing an alternating fluid flowhaving a frequency of velocity variation of at least 20 cycles persecond, a rectifier valve comprising means providing an opening forfluid flow through the valve, and means for controlling fluid flowthrough said opening including an elongated cantilever supported reed ofresilient material, and means on the reed seated on the downstream sideof said opening, the reed having a major and a minor transversedimension and being tapered in the plane of its minor transversedimension longitudinally of the reed over its entire free length, thereed having a lowest undamped natural frequency while immersed in thefluid flowing through said valve which is greater than the frequency ofvelocity variation of said alternating fluid flow.

2. In a pumping system of a type providing an alternating fluid flowhaving a frequency of velocity variation of at least 20 cycles persecond, a rectifier valve comprising means providing an opening forfluid flow through the valve, and means for controlling fluid flowthrough said opening including an elongated cantilever supported reed ofresilient material, and means on the reed seated on the downstream sideof said opening, the reed having a generally rectangular cross sectionto provide the reed with major and minor transverse dimensions and beingtapered in the planes of both the major and minor transverse dimensionover the entire free length of the reed having a lowest undamped naturalfrequency while immersed in the fluid flowing through said valve whichis greater than the frequency of velocity variation of said alternatingfluid flow.

3. In a pumping system of a type providing an alternating fluid flowhaving a frequency of velocity variation of at least 20 cycles persecond, a rectifier valve comprising an elongated hollow housing havinga wall extending longitudinally up the housing to divide the housinginto upstream and downstream passages, that wall being provided withaperture means for the passage of fluid therethrough, and means forcontrolling the flow of fluid through the valve including an elongatedcantilever supported reed of resilient material overlying said wall andaperture means on the downstream side thereof, the reed having major andminor transverse dimensions and being tapered in the planes of both saiddimensions over its entire free length, the reed further having a lowestundamped natural frequency when immersed in the fluid flowing throughthe valve which is greater than the frequency of velocity variation ofsaid alternating flow.

References (Iited in the file of this patent UNITED STATES PATENTS1,796,440 Christensen Mar. 17, 1931 2,064,754 Ivens Dec. 15, 19362,505,757 Dunbar et al. May 2, 1950 2,706,972 Kiekhaefer Apr. 26, 19552,851,054 Campbell Sept. 9, 1958 2,965,123 Hulsander Dec. 20, 1960

1. IN A PUMPING SYSTEM OF A TYPE PROVIDING AN ALTERNATING FLUID FLOWHAVING A FREQUENCY OF VELOCITY VARIATION OF AT LEAST 20 CYCLES PERSECOND, A RECTIFIER VALVE COMPRISING MEANS PROVIDING AN OPENING FORFLUID FLOW THROUGH THE VALVE, AND MEANS FOR CONTROLLING FLUID FLOWTHROUGH SAID OPENING INCLUDING AN ELONGATED CANTILEVER SUPPORTED REED OFRESILIENT MATERIAL, AND MEANS ON THE REED SEATED ON THE DOWNSTREAM SIDEOF SAID OPENING, THE REED HAVING A MAJOR AND A MINOR TRANSVERSEDIMENSION AND BEING TAPERED IN THE PLANE OF ITS MINOR TRANSVERSEDIMENSION LONGITUDINALLY OF THE REED OVER ITS ENTIRE FREE LENGTH, THEREED HAVING A LOWEST UNDAMPED NATURAL FREQUENCY WHILE IMMERSED IN THEFLUID FLOWING THROUGH SAID VALVE WHICH IS GREATER THAN THE FREQUENCY OFVELOCITY VARIATION OF SAID ALTERNATING FLUID FLOW.